Wavelength Division Multiplexing (WDM) offers the most efficient method to exploit the available bandwidth. As the technology progresses the number of feasible channels in the total band is increasing from a handful number to a large number of channels. With tighter channel spacing and wider wavelength bands, the technology is evolving towards Dense WDM, or DWDM.
The DWDM systems now need a large number of laser sources. Large sets of discrete lasers have been used to realize the laser sources required. Multi-wavelength laser sources (MWLS) provide an attractive and cost effective alternative. Wavelength locking is a definite requirement especially for a tightly spaced large set of channels to ensure negligible cross talk and to eliminate any chance of wavelength channels running into each other. As a matter of fact, wavelength locking could be a limiting factor in scaling up the discrete set of lasers to very large sets.
A center wavelength of each laser is usually locked to a standard wavelength such as one proposed in an ITU grid. In an MWLS, a central locking mechanism can establish the locking of the whole set to any grid of interest. The complexity of such a system is much lower than that of a rack of a discrete set of lasers. It is also noted that for a large number of lasers, the driving circuit size might be prohibitive. As a result, a number of subsystems each hosting a subset of channels must be built and then combined. This adds extra loss and other issues such as crosstalk may result from the combiner or multiplexer.